It seems strange that a lumbar puncture is not more noteworthy.

The humble lumbar puncture is in the background, and the honourable mention goes to the cerebrospinal fluid or neurological diagnosis!

I’ve searched medicalnewstoday.com for news items which mention lumbar puncture.  I managed to find about 19 out of 102,000 (that’s only 0.018%) of all their recorded news items! They included a case of rabies, the articles about the MMR vaccination in autism investigation, research into stem cells and an article on brain cancer. There was one mention of my favourite topic - investigation of acute headache.

Here’s the medicalnewstoday.com news feed, which complies with their terms and conditions….

Combination Drug Taken Early Relieves Migraine Symptoms
A combination drug taken within an hour after the start of a migraine is effective in relieving symptoms, according to research published in the July 8, 2008, issue of Neurology®, the medical journal of the American Academy of Neurology.

Canadian Scientists Report On Pain Research At NIDCR's 60th Anniversary Symposium
Nearly everyone has experienced the acute, short-lived pain that occurs after a mild injury, but recent surveys reveal that more than 20% of the population has a chronic pain condition (i.e., pain that has lasted for 3 months or more) and for whic...


Newsfeed display by CaRP

The usual reason for not measuring opening pressure at lumbar puncture is forgetting to include a manometer (pressure guage) in your equipment.

At LP, opening pressure should be measured without exception in the investigation of acute headache. Always remember to measure opening pressure with your patient lying on their side, not sitting upright. The zero point for opening pressure is at the base of the skull, so if you are sitting up and you needle is in the lumbar spine the opening pressure will be at least 30cm (or whatever height the base of the skull is above your needle! If you then add the 10-20cm of intracranial pressure you have a reading in excess of 40cm guaranteed! This is not to be confused with intracranial hypertension, it is a simple but potentially serious error, but it is easy to forget the basics.

When I use Lumbar Puncture to investigate for inflammatory disorders, such as multiple sclerosis, I will deliberately sit the patient up if I don’t have very clear anatomical landmarks, as opening pressure is not crucial in this situation.

However, you need to maintain your skill in Lumbar Puncture with your patient lying on their side, so that if you have to do one for an emergency presentation with headache you have the necesary skill to get the needle inserted with your patient on their side - allowing you to measure opening pressure.

Manometry is the measurement of CSF pressure using a 40cm long plastic gauge. The most common error is not to attemmpt to measure pressure! Measuring pressure is essential in patients presenting with acute headache, as a high or low opeinng pressure may be the only indication that there is a treatable disorder. Idiopathic intracranial hypertension is a disorder of elevated CSF presure, and all other CSF tests will be normal. Similarly, Spontaneous Intracranial Hypotension is a disorder of abnormally low intracranial pressure and all other CSF tests will be normal except for an abnormally low pressure (or CSF is not obtained at all despite good technique - also called a dry tap).

Fact # 4 - always measure opening pressure, it may be the only chance you have to clinch an important diagnosis.

I’ve written my own guideline for doing Lumbar Puncture for my own hospital.  This should reflect best practice.  You can copy this for your own hospital, and adapt it where necessary.  Please remember to quote your source - it is copyrighted, but available for free so long as www.lumbarpuncture.net is acknowledged in your guidance.  Remember that this site contains video links from YouTube so that you are left in no doubt what an LP entails.  Patient information sheet will follow next week.

Here’s the link to the LP Guideline - right click here, then save target as….

22 guage atraumatic needles are now recommended for diagnostic Lumbar Puncture (LP). An atraumatic needle has a rounded tip and is said to avoid cutting the fibres of the dura. If the fibres of the dura are separated without cutting, and the resulting hole is less likely to persist, the risk of causing sustained leak of CSF (cerebrospinal fluid) and low pressure headache is reduced. Some researchers have said that atraumatic needles stil create a tear in the dura, and that it is the local inflammation/healing reaction which reduces the risk of CSF leak.

The issue of needle selection is almost resolved. The most up to date recommendation from the American Academy of Neurology is that 22 guage atraumatic needles should be used, as they are asociated with the lowest risk of an LPs most frequent complication - the post-LP headache. 

The evidence for this comes mostly from anaesthetic literature, but there is little doubt from e.g. good quality studies that an atraumatic needle may reduce post-LP headache from 24% to 12%.

However, not all doctors have ever used atraumatic needles, and the lower risk of post-LP headache should be measured against the risk of a poor patient experience caused by an operator using a needle with which they are not experienced.  A misdirected LP needle can be very painful, particularly if the needle comes into contact with bone (periosteum) or nerve root. This may seem silly i.e. surely all needles are the same?  In actual fact you do get used to the feel of certain needles.  A fine needle is more flexible, whereas you have more control over the direction of a thicker/broader needle. 

There are potentially other methods of preventing post-LP headache.  An interesting way, but not widely accepted, is to insert the needle tangentially i.e. deliberately placing the needle at an angle instead of perpendicular to the surface of the back (see Dr Hatfalvi’s article published in Regional Anesthesia 1995. Tangential insertion also requires training and anatomical knowledge, and image guidance, such as ultrasound, may help less experienced operators.

A preference must surely be for correct use of 22 guage atraumatic needles, but for those of us who are confident with existing cutting or traumatic needles, we will need to justify our continued use of these with evidence of minimal patient discomfort at the actual time of their LP.

The distance from skin to the ligamentum flavum (the tough ligament just befire you reach the epidural space) is between 4 and 7cm in adults. Does anyone know an up-to-date study of this (i.e. if we are getting more obese, is this still true today?)